RAg (R=Pr, Er, Ho)磁性蓄冷材料を用いたGM-冷凍機の冷凍能力

抄録

The refrigeration capacity of a conventional GM refrigerator was studied over a temperature range of 7-25 K by employing a second-stage regenerator stacked in series using different Ag-based regenerator materials, RAg (R=Pr, Er, Ho), together with pure metals, Pb, Cu and Ag. The combinations of PrAg/HoAg and PrAg/Pb stacked as columns in series could reach the lowest temperature of 7.0 K in contrast to that of 7.3 K reached with the conventional Er₃Ni compound, as far as the present refrigerator is concerned. These combinations are in possession of specific heats over the temperature range of 7-25 K, consistently higher than that of Er₃Ni. Moreover, we revealed that, if the amount of PrAg is increased, the replacement of Pb with Ag or Cu at the high-temperature end of the regenerator is possible without affecting the refrigeration capacity of reaching the lowest temperature of 7.0 K. Therefore, we conclude that combinations of PrAg/Ag and PrAg/Cu stacked in stratified form can serve as environment-friendly regenerator materials in the temperature range below 25K.